KVM: selftests: Add helpers to probe for NUMA support, and multi-node systems

Add NUMA helpers to probe for support/availability and to check if the
test is running on a multi-node system.  The APIs will be used to verify
guest_memfd NUMA support.

Signed-off-by: Shivank Garg <shivankg@amd.com>
[sean: land helpers in numaif.h, add comments, tweak names]
Link: https://lore.kernel.org/r/20251016172853.52451-11-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/tools/testing/selftests/kvm/include/numaif.h b/tools/testing/selftests/kvm/include/numaif.h
index 1554003c40a110b5ab4345d974691badb97a4506..29572a6d789cd0bb905ae645ec6b286280eab4f6 100644 (file)
--- a/tools/testing/selftests/kvm/include/numaif.h
+++ b/tools/testing/selftests/kvm/include/numaif.h
@@ -4,6 +4,8 @@
 #ifndef SELFTEST_KVM_NUMAIF_H
 #define SELFTEST_KVM_NUMAIF_H
 
+#include <dirent.h>
+
 #include <linux/mempolicy.h>
 
 #include "kvm_syscalls.h"
@@ -28,4 +30,54 @@ KVM_SYSCALL_DEFINE(mbind, 6, void *, addr, unsigned long, size, int, mode,
                   const unsigned long *, nodemask, unsigned long, maxnode,
                   unsigned int, flags);
 
+static inline int get_max_numa_node(void)
+{
+       struct dirent *de;
+       int max_node = 0;
+       DIR *d;
+
+       /*
+        * Assume there's a single node if the kernel doesn't support NUMA,
+        * or if no nodes are found.
+        */
+       d = opendir("/sys/devices/system/node");
+       if (!d)
+               return 0;
+
+       while ((de = readdir(d)) != NULL) {
+               int node_id;
+               char *endptr;
+
+               if (strncmp(de->d_name, "node", 4) != 0)
+                       continue;
+
+               node_id = strtol(de->d_name + 4, &endptr, 10);
+               if (*endptr != '\0')
+                       continue;
+
+               if (node_id > max_node)
+                       max_node = node_id;
+       }
+       closedir(d);
+
+       return max_node;
+}
+
+static bool is_numa_available(void)
+{
+       /*
+        * Probe for NUMA by doing a dummy get_mempolicy().  If the syscall
+        * fails with ENOSYS, then the kernel was built without NUMA support.
+        * if the syscall fails with EPERM, then the process/user lacks the
+        * necessary capabilities (CAP_SYS_NICE).
+        */
+       return !get_mempolicy(NULL, NULL, 0, NULL, 0) ||
+               (errno != ENOSYS && errno != EPERM);
+}
+
+static inline bool is_multi_numa_node_system(void)
+{
+       return is_numa_available() && get_max_numa_node() >= 1;
+}
+
 #endif /* SELFTEST_KVM_NUMAIF_H */